Which solitaire card game which uses two decks of playing cards?

You're likely thinking of Canfield, a solitaire game that uses two decks of cards.

Here's a brief description:

* Goal: To move all cards to the foundations, building up in suit from Ace to King.

* Setup: Two decks are shuffled and combined. 13 cards are dealt face down to the tableau (the main playing area), forming seven columns with one card face up on each. The rest of the cards are placed face down in a stock pile. Four cards are turned face up to form the waste pile.

* Gameplay: Cards are dealt from the stock pile to the waste pile. You can move cards from the waste pile to the foundations or tableau, building down in descending order by rank, alternating colors (red/black). You can also move face-up cards from the tableau to the foundations or other tableau columns.

* Winning: You win when all cards are successfully moved to the foundations.

Other solitaire games that use two decks of cards:

* Double Klondike: Essentially the same as Klondike solitaire, but with two decks.

* Double Canfield: A variation of Canfield using two decks, often with more challenging rules.

Let me know if you have any other card game questions!